“Yeah well, that engineer don’t know what the fuck they’re talking about.”

In this example, the engineer is the antecedent, the thing that is being referred to previously by the pronoun they. The only difference between the above example and this example

Example with ungendered description:

Bob - “Hey Jo, the engineer thinks we should tweak widget X.”

Me - “Yeah well, they don’t know what the fuck they’re talking about.”

is that the antecedent is in a previous sentence said by a different person. This is a common use case for pronouns in general during a conversation and also a common use case for the singular they. My point is this is not confusion related to the most recent change to the singular they, that restrictions to name and description have been lifted. That's fine, but I think a lot of what people are saying about Shakespeare is relevant to this particular form of confusion, singular they vs plural they, because we have been using the singular they for quite some time.